Support %{c}h for conn-hostname, %h for useragent_host
Submitted by: wrowe
Reviewed by: jim, ylavic, covener
Merge r1818321 from trunk:

"{c}h" exists and logs the value returned by 'ap_get_useragent_host()'.

I'm not sure of the description to write there, so I just mention it in the doc and hope s.o. will find the words :)

This has been introduced in r1730129.
Submitted by: jailletc36
Reviewed by: jim, ylavic, covener


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/branches/2.4.x@1855818 13f79535-47bb-0310-9956-ffa450edef68